1. Field of the Invention
This invention concerns a device for ascertaining the internal pressure in a pressure pipe system, especially in a fuel injection pipe system.
2. Description of the Prior Art
The constant monitoring of internal pressure in a pressure system by means of pressure gauges, e.g. manometric pressure gauges which are included in the pressure system and directly exposed to the pressure medium in the pipes, is common practice in many sectors of industrial technology.
In pipes which do not require constant monitoring, but which instead need only occasional checks of pressure conditions, the provision of a pressure gauge which is permanently included in the system increases assembly work and costs, and is hardly an economically justifiable proposition. This applies, for example, to the testing of pressure conditions in a fuel injection pipeline for diesel engines which is needed only at certain intervals of time or in case of malfunction. The primary objective of such tests is to detect significant points of the injection pressure curve relative to the respective crank angle, with only a secondary interest in measuring absolute pressure values and recording the time-pressure curve in the fuel injection pipes. However, the measuring of pressure in the fuel injection pipes always presents problems in as much as the pressure volume must be broached to allow a pressure gauge to be introduced and the measuring instrument must be screwed directly into the injection pipe. Apart from the awkwardness and inconvenience of such an operation and the considerable loss of time caused thereby, this method entails a further and rather more serious disadvantage. This arises from the high pressures in the fuel injection pipes where it is in most cases very difficult, after repeated disconnection and reconnection of the pipe system for the purpose of introducing and subsequently extracting pressure gauges, to restore every time the vitally important perfect seal for the pipe system as a whole. Most fuel injection pipe connections are not adapted to permit such frequent unscrewing and screwing together again without resulting in defective seals. Moreover, when the threaded joints of the injection pipes are tightened, the high torque which has to be applied for this purpose frequently causes frictional abrasion and dislodgement of small chips of metal. These chips tend to be the cause of recurring trouble in the injection nozzle or jet assembly, chiefly by jamming the jet needle.
In view of these disadvantages there has been a longstanding search for new ways which would allow the internal pressure to be measured, especially in fuel injection pipe systems, without opening up or interrupting the pressure system. Various types of pressure-applying devices have been developed which are usually clamped onto the fuel injection pipe and whereby the internal pressure in the pipe can be ascertained from the resulting elastic deformation of the pipe. However, all previously known forms of such external pressure applying devices were found unsuitable for practical application to different types of engines owing to the differences in the various fuel injection pipe systems and the substantial accelerations and vibrations to which the fuel injection pipes are nearly always exposed.
It is the aim of this invention to provide a means for ascertaining the internal pressure in a pressure system, especially in a fuel injection pipe system, which avoids the disadvantages appertaining to conventional arrangements and which is distinguished by its simplicity, reliability and a minimum of fitting work required for the measuring process.